1. Field of the Invention
The invention relates to a charge-coupled image sensor device for receiving a radiation image and converting the same into an electric signal, wherein a semiconductor body has a number of substantially parallel charge transport channels separated from each other at a major surface at which there is an insulating layer on which a system of electrodes is provided in behalf of the charge transport, wherein the electrode system has windows via which in particular short-wave light of the radiation image can penetrate into the semiconductor body to generate charge carriers therein, and wherein the system of electrodes comprises a first group of electrodes extending in a direction transverse to the direction of charge transport.
The invention relates in addition to a method of manufacturing such an image sensor device.
2. Description of the Prior Art
In such a device a pattern of charge packets corresponding to the radiation or exposure pattern is generated in the radiation-sensitive part and after termination of the integration period can be transferred to a storage register (frame/field transfer). The charge stored in the storage register is then shifted into a shift register line by line from which it is read serially for further processing.
By means of the system of electrodes, depletion regions can be induced in the underlying semiconductor body in which or in the proximity of which charge carriers can be generated by absorption of radiation. These charge carriers can then be stored in the depletion regions below the electrode system in the form of the above-mentioned charge packets.
The sensitivity of such a device can be detrimentally influenced by the system of electrodes. When a metal layer is used in said electrode system, the thickness of the metal must generally be very small since otherwise it becomes impervious to radiation. The provision of such thin metal layers often requires an extra manufacturing step during the production process.
Absorption (and/or reflection) by the electrode system can be prevented by using radiation on the rear side of the semiconductor body. However, this usually requires a complicated and difficult production process.
Another method of increasing the sensitivity of charge-coupled image sensor devices is the use of semiconductor material, for example, for example polycrystalline silicon, for the electrode system. Since the coefficient of absorption of silicon for radiation of shorter wavelength is comparatively high, this improvement, however, is smaller for blue light than for long-wave light.
In published Netherlands Patent Application No. 7610700 which corresponds to U.S. Pat. No. 4,141,024, a charge-coupled image sensor device is shown in which the sensitivity for blue light is increased by providing the common electrode system with windows via which the short-wave light can penetrate into the semiconductor body. These windows are obtained in that recesses adjoining each other are always provided in two successive electrodes, situated transversely to the direction of charge transport. During the manufacture of such electrodes notably during the provision of the recesses, alignment tolerances should be taken into account, which usually is at the expense of the required quantity of semiconductor surface area. Moreover, the resistance at the area of the recesses is larger than in the remainder of the electrodes so that the response time hereof is adversely influenced. Moreover, in the image sensor device shown the window portions are situated above the channel region, which may cause a loss in transport efficiency. If desired, this can be solved by providing a transparent electrode for which, however, process steps not very common in semiconductor technology are required.